1. Field of the Invention
The present invention relates to a process for activating catalysts in a reducing gas atmosphere and impregnating the activated catalysts with an inert melted solid.
2. Background of the Invention
Particulate catalyst compositions which are produced in particular in the form of tablets, extrudates or otherwise pelletized and which, before use, are activated by treatment in a reducing atmosphere, more especially in hydrogen or in a hydrogen-containing gas mixture, are widely used in industry. Such catalyst compositions generally consist of one or more catalytically active components, optionally in conjunction with inert supports. Known catalysts of this type include, in particular, metal and supported metal catalysts which are required and used for various hydrogenation processes. Catalysts of this type are often very sensitive to air in their activity to the point of pyrophoric behavior. Accordingly, stringent requirements have to be satisfied in the manufacture, storage, transport, and use of these catalysts.
In practice, there are various known methods for dealing with the problems involved, including the in situ activation of particulate catalysts in the reactor immediately before their use from shaped, particulate catalyst intermediates and passivation of the activated catalyst by partial re-oxidation. It is also known that powder-form catalyst may be kept in their active form by coating and/or impregnation with a protective composition which is eliminated when the catalysts are used. In catalytic processes of the type in question here, the in situ activation of the catalyst packing of a reactor is often preferred although this does involve serious reductions in the hydrogenation capacity of a plant as well as technical risks.
The production of air-sensitive active catalysts separately from the place and time at which they are used takes place to only a limited extent in practice. In particular, it is known that nickel hydrogenation catalysts can be stabilized by impregnation with solid fats, solid paraffin, fatty amines, or similar products. Thus, German Democratic Republic Patent No. 155,390 for example describes a process for the production of catalysts which consist of pyrophoric metal, optionally on inorganic supports, and which are impregnated with materials melting at temperatures above 315.degree. K. In this process, the molten suspensions of catalyst and impregnating agent are said to be converted by spraying and simultaneous cooling into a fine-grained, free-flowing and air-stable form. French Patent No. 1,555,015 describes powder-form Raney nickel catalysts coated with a protective layer of materials melting at temperatures in the range of from 60.degree. to 100.degree. C., more especially hydrogenated vegetable oils, fatty acids or fatty acid salts, glycols, other polyhydric alcohols, or organic polymers. Solid layers of this type are said to be applied to the catalyst compositions by means of a solvent.